At a Glance

Higher-than-normal ocean water temperatures stress corals and cause them to bleach.The die-offs occurred between 2013 and 2017. Scientists say higher ocean temperatures are a result of global warming.

Bleaching caused by rising sea temperatures has killed more than one third of the coral reefs in the ocean around the Pacific island of Guam, according to a new study.

"Never in our history of looking at reefs, have we seen something ," Laurie Raymundo, director of the University of Guam Marine Lab, said at a press conference Monday, according to the Pacific Daily News.

Raymundo led a group of researchers who began surveying Guam's reefs after a massive, unprecedented coral bleaching event in 2013. They spent four years studying the effects of that event and subsequent bleaching.

Not only did they discover that 34 percent of Guam's reefs were dead, they found that as many as 60 percent of the reefs along the island's coast had died. Their were recently published in the journal Coral Reefs.

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Higher-than-normal ocean water temperatures can , which causes them to lose the algae that gives them their distinct coloring and is their primary food source. Scientists say the upward trend in ocean temperatures is a result of global warming.

"The highest temperatures we've ever recorded in Guam happened in 2017," Raymundo said. "Right now, the best way to stop bleaching is to lower our carbon footprint."

A bleached reef on the eastern coast of Guam.

(University of Guam Marine Laboratory)

Corals in other parts of the world are also at risk. Back-to-back marine heat waves – periods of unusually high ocean temperatures – that occurred in Australia in 2016 and 2017 caused and die-offs over two-thirds of the Great Barrier Reef.

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In Guam, the die-offs between 2013 and 2017 are the of coral reefs to be recorded there in the last five centuries, according to a press release.

“Our reefs are undergoing very dramatic changes – very suddenly – that haven’t been seen in the last 500 years,” Raymundo said in the release. “We need to protect what remains and rehabilitate where we can using whatever means we can because they are essential to the island, both ecologically and economically.”

Corals are vital fish habitats and provide coastal protection, she said. They're also a key tourist attraction on Guam, which had more than 1.5 million visitors in 2018.

The island and the Northern Marianas are currently under a , according to the NOAA Coral Reef Watch, which uses satellites to monitor water temperatures.

Raymundo said that reducing the impacts of pollution, sewage, plastic waste and other human activities would help conserve the reefs, but that climate change is the primary factor in their sudden decline.

"It's what we're pumping into the atmosphere that is creating warmer temperatures," she said at the press conference. "There's enormous countries, with enormous populations, and we know which ones they are, that are responsible for the vast majority of carbon going into the environment. And it's not small islands like Guam, nonetheless, we are affected by it."